Definition
A thin, solid line on an engineering or aircraft drawing that shows the measured distance between two points, surfaces, or features. It is terminated at each end by an arrowhead touching an extension line, with the numerical measurement placed in a break in the line or just above it.
Plain English
The line on a drawing that tells you how long, wide, or far apart something is. It has arrows at each end and a number showing the actual size.
Context Anchor
Seen on aircraft drawings, maintenance diagrams, installation instructions, and other technical drawings that show sizes or locations.
Derivation
From the Latin 'dimensio' meaning 'a measuring.' A dimension line is literally the line that carries the measurement.
Why Pilots Care
When reading aircraft documents or diagrams, recognizing a dimension line helps you separate the measured size from the actual outline of the part or area being shown.
Intuition Check
Do not read a dimension line as an edge, wire, or aircraft part. It is a measuring mark on the drawing that shows what distance the number applies to.
Example Sentence 1
The technician checked the dimension line on the repair drawing to confirm the rivet spacing was 1.5 inches.
Example Sentence 2
Always verify the dimension lines before fabricating a new bracket for the airframe.